Throughout the civilized world there is a growing need to make more efficient use of the supply of electrical power. With this increasing interest in energy conservation, methods for centralized control of electrical loads that are uncomplicated and cost-effective to install are becoming more important. Using lighting loads as an example, one effective way to reduce energy consumption is to use dimmable lighting systems. Newer lighting systems control light output and energy consumption by adjustment of lighting levels throughout the day, reducing energy usage when light is not needed.
The growing imposition of time-of-day dependent utility rates presents another important economic rationale for curtailing consumption to avoid onerous penalties for excessive peak loads. As electric power generation capacity becomes less able to meet periods of excessive demand, consumers are becoming more accepting of utility provisions to automatically reduce load demands rather than experience a brownout.
Load control systems utilizing separate dedicated wiring have been widely employed for energy and comfort management in new commercial buildings. However, costs of adding the required control wiring usually prohibits such load control upgrades to be retrofit to existing buildings. A cost-effective wireless system would, however, mitigate the complications of the routing of new wiring that would be required.
Historically, remote load management was implemented through the use of physical control wires that interconnected an automatic or manual controller with each load (e.g. lighting fixture) under its control. However, when applied to lighting control, the requirement for new dedicated control wiring proved to be excessively costly in those instances where lighting controls were to be added after the original building construction. And, even in the case of new construction, attractive reduction of installation costs can often be realized by utilizing the power wiring infrastructure as a communications medium for environmental building control signals.
Due to the considerable quantity of lighting fixtures that are employed in most buildings, it is important that the per-fixture cost of dimming be reduced as much as possible. To satisfy this requirement, several wireless control communication techniques have been put into practice. One such approach uses dimming signals that are transmitted by phase-cut manipulation of the power supplied to specially equipped fixtures on an existing lighting branch. For example, Philips Advance Transformer Mark X® and Lutron TuWire® ballasts use phase cut manipulation. Typically, wall-mounted dimmers, such as those usually employed for incandescent loads, are then used for manual dimming control with phase cut manipulation. This method has proved very convenient for small areas, but not for wide application because power quality is incrementally reduced by each fixture under such control.
There has been a longstanding need for a reliable, low-cost means of communicating load management commands in commercial applications. Use of the existing power lines for this purpose always seemed to offer a very attractive solution. The traditional approach to meet this goal attempted to use a variant of power line carrier control (“PLC”). PLC involves superimposing a coded carrier frequency in the range 100 kHz to 2 MHz or a timed burst of noise onto the AC power line. Systems employing PLC have seen widespread use in residential lighting applications, but limited penetration in commercial lighting applications. Osram-Sylvania introduced a commercial PLC control system for demand response applications, under the designation of PowerSHED®. However, the system has yet to achieve significant market acceptance.
Still another general approach to remote load control uses radio frequency signaling. For this approach, control messages in the form of radio frequency signals are transmitted via a mesh network, where they are handed off sequentially though low-power transceivers located at each control point. However, a low-cost implementation of this approach capable of communicating control messages has been illusive.